The most common computer pointing devices include computer mouse and tracking balls. Both are classified as electronic type, optic type and semi-optic type. The electronic type pointing device or mouse comprises a ball or spherical member which is rollingly movable with respect to two variable resistors respectively representing two orthogonal axes defining the plane of the monitor screen. The rolling movement causes the variable resistors to change their resistance and thus providing a signal indicating the displacement associated with the monitor cursor in the two axes. A disadvantage of the electronic type pointing device is that it is less precise. Further, the variable resistors may be subject to oxidation when exposed in the atmosphere.
The optic type pointing device uses photo-transistors to replace the rolling movement of the spherical member of the electronic type mouse. A disadvantage associated with the optic type mouse is that the photo-transistors are very easy to be damaged. Further, the optic mouse has to be operated on a dark pad and is more costly.
The semi-optic type pointing device takes advantages of the benefits of both the electronic type and the optic type, using the rolling motion of a spherical member to drive rotatable means which are associated with two sets of light emitting diode and photo-transistor to convert the rolling motion of the spherical member into electrical signals. The advantages of the semi-optic type mouse are that it has a good precision, that it is only moderately cost and that it has a longer service life. Thus, most of the computer mouses available in the market are of the semi-optic type.
A problem associated with the semi-optic type computer mouse is that the spherical member of the mouse is in general in contact engagement with two rotatable shafts to drive the shafts in order to convert the rolling motion of the spherical member into electrical signals. The contact engagement, however, inevitably causes un-desired displacement of the shafts. This deteriorates the precision of positioning the cursor in the monitor screen, especially in handling high precision drawings.
Further, the spherical member of the mouse is generally rolling on for example a mouse pad. Dusts and ashes may be brought into the mouse by adhering to the surface of the tracking ball during the rolling motion thereof. Such dusts may get stuck to the shafts by being brought into contact with the shafts by the spherical member. This may eventually result in an improper operation of the conversion of the rolling motion of the spherical member into electrical signals. Thus it requires frequent and periodic cleaning of the shafts and the spherical member.
In addition, in operating a mouse, the user has to continuously move the mouse relative to the mouse pad or a fixed surface with his or her hand. This may cause strain of the wrist muscle, especially for using mouse for a long while.
Moreover, the relationship between the motion of the spherical member relative to the mouse pad and the movement of the cursor in the monitor screen is in general not consistent. Thus, a user has to get acquaint with the relationship before he or she may operate the mouse well. This is very inconvenient for the user.
Thus, it is desirable to have an improved computer pointing device which overcomes the problems encountered in the conventional pointing devices or mouses.